Voltage divider for variable magnification electron microscopes



Sept. 18, 1951 BRUCK VOLTAGE DIVIDER FOR VARIABLE MAGNIFICATION ELECTRON MICROSCOPES Filed Jan. 13, 1948 INVENTOR V l/I/A V l/l/ I W2 A RNEY Patented Sept. 18, 195i PATENT VOLTAGE DIVIDER FOR VARIABLE MAGNI- FICATION ELECTRON MICROSCOPES Application January 13, 1948, Serial No. 2,075 In France December 24, 1946 Section 1, Public Law 690, August 8, 1946 Patent expires December 24, 1966 2 Claims. l

A theoretically simple process for varying the magnification in an electron microscope consists in varying the focal distance of its lens. The desired variation of that focal distance can be obtained, either by changing the intensity of the current supplied to the lens (if the device is a magnetic microscope). or by operating on the potential of the central electrode of the said lens (if the device is an electrostatic microscope).

But, in the case of an electrostatic microscope, a very high tension voltage divider must necessarily be available, a condition which results, with the conventional means of realization, in

the adoption of a heavy and cumbersome equipment, which moreover necessitates a large amount of current.

For overcoming the above drawbacks, I provide the electrostatic microscope, according to the present invention, with a voltage divider consisting merely of a semi-conductor presenting a relatively high resistance of the order of 10 ohms, the nature and the dimensions of which have been properly determined. As a result, indeed, of my experimental work in the field under consideration, I have observed that it was quite possible to obtain well defined intermediate potentials by making use of semi-conductors presenting a relatively high resistance of the order of 10 ohms.

Considering the case, for instance, of an electrostatic microscope the lens of which oiiers an internal resistance amounting to x10 ohms, I can adopt a voltage divider made out of a Bakelite or marble stick about 50 cm. long ofiering a suillciently small resistance (of the order of ohms) in comparison with the internal resistance oi the lens.

It can be stated non-limitatively and as an instance of a simple means of obtaining broadly varying magnification factors, that a voltage divider can conveniently be made out of a semiconducting tubular stick I (Fig. 1) of Bakelite or of marble, solid or hollow, of about 1 meter long and 1 cm. or so in diameter. One of the ends of that stick (2, Fig. 1) is grounded, while the other end 9 is connected to the negative high voltage source, of the order for instance of -50 kv. Moreover, the central electrode 5 of the lens 9 of the electron microscope is connected to a ring l (metallic or semi-conducting), which slides on the stick i.

It is obviously possible to choose, for the semiconductor under consideration, many shapes and dispositions of a very different character. There is shown, in Fig. 2 a form of realization according to which the variable section of the semi-conductor is made out of a semi-conductor circular section i on which carries the terminal part of a movable handle 8, while the negative high potential end of the same semi-conductor is the terminal part 9 of the circular section 1. The rotary device shown in the Fig. 2 is more particularly suitable, namely, for the applications in which it is deemed sufiicient to obtain limited variations only of the magnification factor.

Lastly, though my invention is specially intended for the electrostatic variable magnification microscopes, there is no impossibility to use it in all the electronic apparatus in which it is advisable to adjust or control electrode potentials corresponding to zero intensity of output current.

What I claim is:

1. A voltage divider, particularly adapted for the feed of the electrodes of electrostatic lenses of electronic microscopes, comprising a movable part and a fixed part, the said fixed part consisting of a bar of semi-conducting material presenting a relatively high resistance comparable with the resistance between the electrodes of the electrostatic lenses and being fed at its ends by a high voltage source said movable part being in electrical contact with said fixed part on a length which is much smaller than the length of the latter.

2. A voltage divider as set forth in claim 1. wherein the said fixed part consists of a tubular bar of semi-conducting material presenting a relatively high resistance comparable with the resistant a between the electrodes of the electrostatic lenses and in which the said movable part consists of a ring able to slide from one end to the other of the said fixed part, the variable voltage according to the position of the said ring on the said fixed part being tapped on the said ring.

HENRI BRUCK.

REFERENCES CITED The following references are of record in the file oi this patent:

' UNITED STATES PATENTS Clark Oct. 12, 1948 

